The embodiment described herein relates to a non-contact type shaft sealing device for sealing a space between a rotational shaft and a housing of a device that will be shaft-sealed, such as a turbine, a blower, a compressor, an agitator, or a rotary valve.
A non-contact type shaft sealing device of the aforementioned type is disclosed in publications, for example, a Japanese Unexamined Patent Application Publication No. 4-171370. Hereinbelow, an example device of this type will be described with reference to FIGS. 1 and 2. In FIG. 1, reference numeral 1 denotes a rotational shaft of a device that will be shaft-sealed. A rotational seal ring 2 is hermetically fitted about the rotational shaft 1. A fixing-side seal unit 5 is connected to a housing 4 of the device that will be shaft-sealed. In the unit 5, a stationary sealing ring 9 is disposed to face the rotational sealing ring 2 in the axial direction. Mutually opposing surfaces of the stationary sealing ring 9 and the rotational sealing ring 2 are formed as sealing surfaces 9s and 2s. 
On the opposite side of the sealing surface 9s of the stationary sealing ring 9, springs 11 for urging the stationary sealing ring 9 toward the rotational sealing ring 2 are provided. The stationary sealing ring 9 has air inlets 9b formed from a peripheral surface thereof so as to reach the sealing surface 9s. Through the air inlets 9b, a barrier gas, such as a nitrogen gas, is supplied from an outside source to the sealing surface 9s. 
Orifices 12 are provided in the air inlets 9b to reduce variations in supply pressure of the barrier gas. In addition, as shown FIG. 2, the sealing surface 9s has a plurality of, for example, six arcuate pocket grooves 9c formed at identical pitches along a circle line extending substantially along the center between the inner and outer peripheries. Each of the air inlets 9b opens at a circumferentially central portion of each of the pocket grooves 9c. Thus, in the configuration shown in the drawings, the six air inlets 9b each containing the orifice 12 are formed in the stationary sealing ring 9.
In the structure as described above, the barrier gas supplied from an outside source is throttled by the orifices 12, and is then fed to the individual pocket grooves 9c through the air inlets 9b. The gas is led to pass through the gap between the sealing faces 2s and 9s (which will be referred to as an inter-sealing-surface gap, hereinbelow) of the respective rotational sealing ring 2 and the stationary sealing ring 9. Then, the gas flows out of the pocket grooves 9c toward the inner and outer peripheries. At this time, a gas pressure is built on the inter-sealing-surface gap, and it works as a force that presses the stationary sealing ring 9 in the opening direction (leftward in the drawing). The stationary sealing ring 9 is held at the position where the aforementioned gas-pressure force antagonizes spring forces exerted by the springs 11 (specifically, the spring forces include axial pressing forces of internal gas pressures). Accordingly, the stationary sealing ring 9 is held in the state of non-contacting the rotational sealing ring 2. Thus, shaft-sealing can be implemented using the barrier gas that fills the space between the sealing faces 2s and 9s. 
When the inter-sealing-surface gap in the force-antagonized state is widen because of mechanical vibrations or the like, an open-directional force is reduced to thereby move the stationary sealing ring 9 in the direction where the inter-sealing-surface gap is narrowed. In contrast, when the inter-sealing-surface gap is narrowed, the stationary sealing ring 9 moves in the direction where the inter-sealing-surface gap is widened. That is, the device has a self gap-adjusting function.
The pressure in the inter-sealing-surface gap increases in proportion to an increase in the number of the air inlets 9b and in the orifice diameter. Therefore, the sealed condition described above can be more secure in proportion to the increase. However, the increase widens the inter-sealing-surface gap. In order that the self gap-adjusting function works even more favorably, the device is manufactured by setting the inter-sealing-surface gap in a range that allows a quick corrective operation to be performed in response to a variation in the gap.
The conventional non-contact type shaft sealing device manufactured as described above, however, consumes an increased amount of the barrier gas. Therefore, the device has a problem in that it is not sufficient to provide economic advantages. That is, for the device manufactured only in consideration of the improvement in sealing characteristics, the number of the air inlets 9b and the bore diameter of each of the orifices must be increased to be excessively large. This results in the increase of barrier-gas consumption, reducing economical characteristics. To narrow the inter-sealing-surface gap, stronger springs 11 must be disposed behind the stationary sealing ring 9. In this case, however, the barrier-gas pressure distribution on the inter-sealing-surface gap can vary greater. Furthermore, the bore diameters of the air inlets 9b and the orifices 12 must also be checked and must be changed to be suitable.
Thus, conventional devices are not structured sufficient to provide economical advantages in barrier-gas consumption. Although there are devices structured in consideration of this problem, designing and manufacturing procedures thereof are complicated.
The embodiment disclosed herein is made in view of the above-described problems with the conventional cases. Accordingly, an advantage of the embodiment is to provide a non-contact type shaft sealing device that allows barrier-gas consumption to be minimized, thereby providing economical advantages.
A non-contact type shaft sealing device described herein comprises a stationary sealing ring disposed to axially oppose a rotational sealing ring provided on a rotational shaft of a device that will be shaft-sealed, and urging means for pressing the stationary sealing ring toward the rotational sealing ring, wherein a barrier gas is fed to space between mutually-facing sealing surfaces of the stationary sealing ring and the rotational sealing ring via a plurality of air inlets formed in the stationary sealing ring. The non-contact type shaft sealing device has a number n of the air inlets in a range of 3 to 24; a bore diameter d of a throttling mechanism provided in each of the air inlets in a range of 0.05 to 3 mm; and a dimensionless quantity xcex1 defined as
xcex1=8 hD/nd2
where, h=inter-sealing-surface gap, and
D=shaft diameter,
in the range of 1xe2x89xa6xcex1xe2x89xa6200.
The dimensionless quantity xcex1 represents the relationship among the number n of the air inlets provided in the stationary sealing ring, the bore diameter d of the throttling mechanism formed of either an orifice or a drilled opening which is provided in each of the air inlets, and the amount of gas leaking through the sealing surfaces. By setting the dimensionless quantity xcex1 to be within the aforementioned range, the non-contact type shaft sealing device, in which stabled sealing characteristics are ensured, and barrier-gas consumption is minimized, is provided.
When the dimensionless amount xcex1 is 15xe2x89xa6xcex1xe2x89xa6160, the device is further improved in characteristics regarding sealing performance and barrier-gas consumption. Furthermore, when the shaft diameter D is in a range of 10 to 500 mm, the aforementioned sealing characteristics and the barrier-gas consumption characteristics can be even more securely obtained.